Conventionally, a charging circuit is known that is connected to a constant voltage source to charge a secondary battery with the supply voltage of the constant voltage source and includes a thermistor to detect the temperature of the secondary battery as a change in resistance and a voltage detection part to detect a voltage at one end of the thermistor being lower than or equal to a predetermined low voltage, where the charging circuit stops charging the secondary battery with the supply voltage of the constant voltage power supply in response to the voltage detection part detecting the voltage being lower than or equal to the predetermined low voltage. (See, for example, Patent Document 1.)
[Patent Document 1] Japanese Laid-Open Patent Application Publication No. 2004-274871